After you reg an account you can immediately start playing by clicking on the 'Start Playing' button on the main page hehe.
Not only do you play against other people but you passively complete quests to unlock more guys whilst you play. The quest requirements and progress are saved in real time and are kept track via the 'Ninja Missions' button.

If at anytime you dont like your score or wish to have a lower rank simply to get a newbee quest out of the way, you can reset all your stats/rank/wins via your account. Resetting resets everything except mission progress.